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Always choose an appropriate transparent color.
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Usually we try to use the "traditional" Doom transparency index, #247,
but there are some rare cases (notably in doom2.wad's TITLEPIC) where
that color is actually used as part of the image. So we always make
sure to check that the transparency index isn't used in the actual
picture data, and if it is, we pick a different color.

Fixes #25.
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@fragglet
fragglet committed Aug 10, 2024
1 parent 973f437 commit f6d8e5a
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Showing 4 changed files with 108 additions and 13 deletions.
111 changes: 104 additions & 7 deletions src/conv/graphic.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,95 @@ VFILE *V_FlatFromImageFile(VFILE *input, const struct palette *pal)
return result;
}

static bool HasTransparency(const struct patch_header *hdr,
const uint8_t *srcbuf, size_t srcbuf_len)
{
uint32_t *columnofs =
(uint32_t *) (srcbuf + sizeof(struct patch_header));
int x, y, expect_y, off, cnt;

if (hdr->height > 255) {
return true;
}

// Each column must consist of consecutive post(s) that cover the
// entire space of the picture.
// TODO: wadptr in the future might put posts out of order to achieve
// better compression, in which case this might mistakenly identify
// some pictures as having transparency.
for (x = 0; x < hdr->width; ++x) {
off = columnofs[x];
SwapLE32(&off);
expect_y = 0;
while (srcbuf[off] != 0xff) {
y = srcbuf[off];
if (y != expect_y) {
return true;
}
cnt = srcbuf[off + 1];
expect_y += cnt;
off += 4 + cnt;
}
if (expect_y != hdr->height) {
return true;
}
}

return false;
}

#define SET_BIT(bitset, idx) \
do { bitset[(idx) / 32] |= 1 << ((idx) % 32); } while(0)
#define BIT_IS_SET(bitset, idx) \
((bitset[(idx) / 32] & (1 << ((idx) % 32))) != 0)

static int TransparencyColor(const struct patch_header *hdr,
const uint8_t *srcbuf, size_t srcbuf_len)
{
uint32_t used_colors[8];
uint32_t *columnofs =
(uint32_t *) (srcbuf + sizeof(struct patch_header));
uint32_t off;
int x, y, i, cnt;

// Examine every pixel in the image; used_colors will be the result,
// a bit-set indicating which colors have been found.

memset(used_colors, 0, sizeof(used_colors));

for (x = 0; x < hdr->width; ++x) {
off = columnofs[x];
SwapLE32(&off);
while (srcbuf[off] != 0xff) {
y = srcbuf[off];
cnt = srcbuf[off + 1];
off += 3;
for (i = 0; i < cnt; i++, y++) {
SET_BIT(used_colors, srcbuf[off]);
off++;
}
off++;
}
}

// Try Doom's duplicate black color, "traditionally" used by modders
// as the transparency color.
if (!BIT_IS_SET(used_colors, 247)) {
return 247;
}

// Otherwise, look for any color that doesn't appear in the image.
for (i = 255; i >= 0; i--) {
if (!BIT_IS_SET(used_colors, i)) {
return i;
}
}

// TODO: Uh oh, now we're in trouble.

return 0;
}

static bool ValidatePatch(const struct patch_header *hdr,
const uint8_t *srcbuf, size_t srcbuf_len)
{
Expand Down Expand Up @@ -254,14 +343,14 @@ static bool ValidatePatch(const struct patch_header *hdr,
}

static void DrawPatch(const struct patch_header *hdr, uint8_t *srcbuf,
size_t srcbuf_len, uint8_t *dstbuf)
size_t srcbuf_len, uint8_t *dstbuf, int trans_color)
{
uint32_t *columnofs =
(uint32_t *) (srcbuf + sizeof(struct patch_header));
uint32_t off;
int x, y, i, cnt;

memset(dstbuf, PALETTE_TRANSPARENT, hdr->width * hdr->height);
memset(dstbuf, trans_color, hdr->width * hdr->height);

for (x = 0; x < hdr->width; ++x) {
off = columnofs[x];
Expand All @@ -287,6 +376,8 @@ VFILE *V_ToImageFile(VFILE *input, const struct palette *pal)
uint8_t *buf, *imgbuf = NULL;
struct patch_header hdr;
size_t buf_len;
bool has_transparency;
int transparent_color = 0;
VFILE *result = NULL;

buf = vfreadall(input, &buf_len);
Expand All @@ -303,9 +394,15 @@ VFILE *V_ToImageFile(VFILE *input, const struct palette *pal)
goto fail;
}

DrawPatch(&hdr, buf, buf_len, imgbuf);
has_transparency = HasTransparency(&hdr, buf, buf_len);
if (has_transparency) {
transparent_color = TransparencyColor(&hdr, buf, buf_len);
}

DrawPatch(&hdr, buf, buf_len, imgbuf, transparent_color);

result = V_WritePalettizedPNG(&hdr, imgbuf, pal, true);
result = V_WritePalettizedPNG(&hdr, imgbuf, pal,
has_transparency, transparent_color);

fail:
free(imgbuf);
Expand Down Expand Up @@ -334,7 +431,7 @@ VFILE *V_FlatToImageFile(VFILE *input, const struct palette *pal)
hdr.height = buf_len / 64;
hdr.topoffset = 0;
hdr.leftoffset = 0;
result = V_WritePalettizedPNG(&hdr, buf, pal, false);
result = V_WritePalettizedPNG(&hdr, buf, pal, false, 0);

fail:
free(buf);
Expand All @@ -358,7 +455,7 @@ VFILE *V_FullscreenToImageFile(VFILE *input, const struct palette *pal)
hdr.height = FULLSCREEN_H;
hdr.topoffset = 0;
hdr.leftoffset = 0;
result = V_WritePalettizedPNG(&hdr, buf, pal, false);
result = V_WritePalettizedPNG(&hdr, buf, pal, false, 0);
free(buf);

return result;
Expand Down Expand Up @@ -440,7 +537,7 @@ VFILE *V_HiresToImageFile(VFILE *input)

hdr.width = HIRES_SCREEN_W;
hdr.height = HIRES_SCREEN_H;
result = V_WritePalettizedPNG(&hdr, screenbuf, &palette, false);
result = V_WritePalettizedPNG(&hdr, screenbuf, &palette, false, 0);

free(screenbuf);
free(lump);
Expand Down
2 changes: 1 addition & 1 deletion src/conv/palette.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ VFILE *V_ColormapToImageFile(VFILE *input, const struct palette *pal)
hdr.height = buf_len / 256;
hdr.topoffset = 0;
hdr.leftoffset = 0;
result = V_WritePalettizedPNG(&hdr, buf, pal, false);
result = V_WritePalettizedPNG(&hdr, buf, pal, false, 0);

fail:
free(buf);
Expand Down
4 changes: 2 additions & 2 deletions src/conv/vpng.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -303,7 +303,7 @@ static png_color *MakePNGPalette(const struct palette *palette)

VFILE *V_WritePalettizedPNG(struct patch_header *hdr, uint8_t *imgbuf,
const struct palette *palette,
bool set_transparency)
bool set_transparency, int transparent_color)
{
png_color *png_pal = MakePNGPalette(palette);
VFILE *result = NULL;
Expand All @@ -324,7 +324,7 @@ VFILE *V_WritePalettizedPNG(struct patch_header *hdr, uint8_t *imgbuf,
if (set_transparency) {
alphabuf = checked_malloc(256);
memset(alphabuf, 0xff, 256);
alphabuf[PALETTE_TRANSPARENT] = 0;
alphabuf[transparent_color] = 0;

png_set_tRNS(ctx.ppng, ctx.pinfo, alphabuf, 256, NULL);
}
Expand Down
4 changes: 1 addition & 3 deletions src/conv/vpng.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,6 @@

#include <png.h>

#define PALETTE_TRANSPARENT 247

struct png_context {
png_structp ppng;
png_infop pinfo;
Expand All @@ -28,4 +26,4 @@ void V_ClosePNG(struct png_context *ctx);
uint8_t *V_ReadRGBAPNG(VFILE *input, struct patch_header *hdr, int *rowstep);
VFILE *V_WritePalettizedPNG(struct patch_header *hdr, uint8_t *imgbuf,
const struct palette *palette,
bool set_transparency);
bool set_transparency, int transparent_color);

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